Can grave's disease affect a pregnant woman?

Yes: Yes, not only high thyroid state can affect the pregnant mother but also the unborn fetus. Check with your endocrinologist that you are on proper treatment and close monitoring.

It affects everyone: Graves' can occur in anybody so it can affect pregnant woman as well, however, pregnancy is an immunosuppressive state so it's possible that the graves' disease will get better during the pregnancy and get worst after the delivery.